Recent advance in neuroscience is making clear the natural shape of neutrotransmitters, substances deeply related to memory in the brain. It is said that some of these substances are neuropeptides containing prolines.
Recovery of the memory was reported by the dose of neuropeptide containing proline to an experimental amnesia rat (See Science 211, 601 (1981)).
On the other hand, it is presumed that these neuropeptide-hormones shall be metabolized by cerebral endogenous peptidases. Especially, prolyl endopeptidase (EC, 3. 4. 21. 26) might take part in this metabolism closely (See J. Biochem., 94, 1179 (1983)).
From these facts, the studies were in progress that it should be possible to prevent or treat amnesia by inhibiting prolyl endopeptidase and suppressing the metabolism of neutrotransmitters. (See Protein, Nucleic acid and Enzyme 25(6), 513(1980); Nippon Nougei Kagaku Kaishi 58(11), 1147(1984); J. Neurochem., 41, 69(1983); ibid 42, 237(1984).)
For the purpose described above, several compounds were synthesized. For example, it is clear that N-benzyloxycarbonyl-glycyl-L-proplyl-chloromethane, N-benzyloxycarbonyl-L-prolyl-prolinal strongly inhibit prolyl endopeptidase (See J. Neurochem., 41, 69 (1983)). More recently, it is disclosed that compounds shown below are effective for the above purpose.
(i) Prolinal derivatives of general formula: ##STR3## [wherein A represents a protecting group of amino acid group in the field of amino acid chemicals, and X represents a residual group of an amino acid.]
See Japanese Patent Kokai No. 60-188317, i.e. European Patent Publication No. 154353.
(ii) N-acylpyrrolidine derivatives of general formula: ##STR4## [wherein n represents a number of 1.about.4, and R represents lower alkyl ester group, --CH.sub.2 OH group or aldelyde group.]
See Japanese Patent KoKai No. 61-37764; a compound wherein n is 5 is also disclosed by correction, i.e. European Patent Publication No. 172458.
(iii) Compounds of general formula: ##STR5## [wherein A represents methyl group or benzyloxy group, R represents isopropyl group or isobutyl group on condition that plural R's are of the same meaning in one formula. And n represents 2 or 3.]
See Japanese Patent Kokai No. 61-183297.
Most recently, five applications related to anti-amnesia agents having prolinal skeltons were published.
(iv) Compounds of general formula: ##STR6## [wherein R represents a group of --CH.sub.3, ##STR7## See Japanese Patent Kokai No. 61-238775, i.e. European Patent Publication No. 201741.
(v) N-acylpyrrolidine derivatives of general formula: ##STR8## [wherein R.sup.3 represents lower alkyloxycarbonyl group, hydroxymethyl group or formyl group, R.sup.1 represents a hydrogen atom or lower alkyl group, R.sup.2 represents phenyl group or a group of the following general formula: ##STR9## (wherein R.sup.4 represents a hydrogen atom, a halogen atom or lower alkoxy group, R.sup.5 represents a hydrogen atom or lower alkyl group, n represents 0 or 1, A represents an oxygen atom, methylene group, hydroxymethylene group, phenylmethylene group or carbonyl group.) or R.sup.1 and R.sup.2 represent, together a benzylidene group unsubstituted or substituted by aromatic ring(s).]
See Japanese Patent Kokai No. 61-238776, i.e. European Patent Publication No. 201742.
(vi) Compounds of general formula: ##STR10## [wherein n represents a number of 0.about.2. R.sup.1 represents a straight-chained organic group of from 5 to 25 carbon atoms which is saturated or unsaturated, wherein an unsaturated carbon chain may contain a plural number of double bonds. R.sup.2 represents a group of ##STR11## R.sup.3 represents lower alkyl ester group, --CH.sub.2 OH group or aldelyde group.]
See Japanese Patent Kokai No. 61-238799, i.e. European Patent Publication No. 201743.
(vii) Compounds of general formula: ##STR12## [wherein n is an integer of more than one, R.sub.1 is a saturated or unsaturated straight-chained hydrocarbon group of from 5 to 25 carbon atoms. Herein, said unsaturated carbon chain may contain a plural number of double bonds. R.sup.3 represents lower alkyl ester group of the formula: --COOR.sup.4 (wherein R.sup.4 represents lower alkyl group.), hydroxymethyl group or formyl group, R.sup.2 represents methyl group, phenyl group, hydroxyphenyl group, indolyl group, imidazolyl group, carboxyl group, formyl group, amino group, hydroxy group, hydroxyalkyl group, thiol group, methylthio group or guanidino group, etc., and each of above groups may be substituted. R.sup.5 represents a hydrogen atom or a single bond between carbon atom and nitrogen atom together with R.sup.2 when n is 3.]
See Japanese Patent Kokai No. 62-84058, i.e. European Patent Publication No. 201743.
(viii) Dipeptide derivatives of general formula: ##STR13## [wherein m represents an integer of 1.about.8, n represents an integer of 1.about.6, R.sup.1 represents a hydrogen atom, R.sup.2 represents a hydrogen atom, a branched alkyl group of from 3 to 5 carbon atoms, phenyl group, hydroxyphenyl group, indolyl group, imidazolyl group or methylthio group, or a single bond between carbon atom and nitrogen atom together with R.sup.2. R.sup.3 represents lower alkyl ester group, hydroxymethyl group or formyl group.]
See Japanese Patent Kokai No. 62-148467, i.e. European Patent Publication No. 201741.